A network's topology describes the layout of the network and determines to a large extent how communications are routed from node to node on the network. Common examples of topologies include: star topologies, where communications are routed through a central or “master” node; bus topologies, where each node is connected to a common backbone or “bus”; and ring topologies, where each node is connected to two other nodes in a circular ring. A common feature of such topologies is that routing communications between participating nodes is relatively simple, the route from one node to another is typically dictated unambiguously by the topology itself.
Meshed topologies have layouts where at least some of the nodes have multiple possible paths to other nodes. Accordingly, they require routing logic to determine a preferred route for communication between two nodes. Such logic may include consideration for a number of factors including, for example, bandwidth, line quality, and the number of “hops” between the participating nodes. Typically, a distributed method may be implemented wherein some or all of the participating nodes periodically poll the “visible” network, i.e. the other nodes with which the polling node may effectively communicate. The polling results are then analyzed in order to at least partially optimize routing between the nodes.
G.hn data networks are designed to leverage previous investment in a home by operating over existing wiring typically found in homes, such as, for example, telephone wiring, coaxial cables and power lines. There is, however, a tradeoff for such leveraging. G.hn networks coexist with other technologies using the same wiring and the network's physical topology may typically be designed and implemented in accordance with the requirements of those technologies. For example, telephone wiring typically carries other analog and/or digital traffic and its coverage of the home may be limited—some rooms may not even have an outlet. Powerline implementations may be exposed to frequent power surges or spikes in accordance with the usage patterns of appliances sharing the same medium. Under such circumstances there may be frequent interference on the G.hn network.
Reference is now made to FIG. 1A which illustrates an exemplary topology 100 for a typical G.hn network. Areas A, B and C represent different logical areas within the network. Each such area represents a “fully meshed” subset of the network; each node in a given area may generally be capable of directly communicating with every other node in the same area. For example, nodes 10, 11, 12 13, 14, and 15 may all be in area A and capable of communicating with each other. Similarly, nodes 14-20 and nodes 19-23 may be in areas B and C respectively. The areas may overlap such that some nodes may be associated with more than one area. For example, nodes 14 and 15 may be in overlap area D, and may therefore directly communicate with each of the other nodes in both areas A and B.
There are instances of multiple possible routes between nodes in topology 100. For example, node 10 may use either node 14 or node 15 to “relay” a transmission to node 18. In fact, even if two nodes may be in the same area and therefore capable of direct communications, there may be other, possibly preferable, routing options. For example, the line between node 10 and node 13 may suffer from interference and/or have relatively low bandwidth. Such interference may be intermittent such that the connection between the nodes is unreliable. If, for example, topology 100 describes a powerline network, there may be a refrigerator located on the line between nodes 10 and 13. As the refrigerator's compressor turns on and off, the power on the line may surge and the connection between the nodes may temporarily break, or the effective rate may be lowered. In such a case, it may be preferable to route their mutual transmissions via node 11, even though a direct transmission path may at least nominally exist.